From command line, to check Windows Firewall rules for 1723 port:
netsh advfirewall firewall show rule name=all | find "1723"
If you have no results, there are no references to any 1723 port (supposedly not blocking).
If yes, try to search more details about the involved rule. For example:
netsh advfirewall firewall show rule name=all > AllPorts.txt
AllPorts.txt file and search for
1723 to obtain more info.
To check GRE protocol, try:
netsh advfirewall firewall show rule name=all | find "gre" /i
and repeat the procedure.
Of course, you are always supposed to be able to perform this search at Windows Firewall screen, on Windows Control Panel.
NOTE: I assume you are talking about checking outgoing 1723 TCP port
and outgoing GRE protocol. Incoming firewalling rules are only needed
if you have some VPN server running inside your computer.